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Garn Owners - please give me some advice

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by sjfrench, Nov 8, 2013.

  1. sjfrench

    sjfrench New Member

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    I'm getting close to finishing the Garn. We will run 1" pex tomorrow. Here's my question.

    Did anyone use a mixing valve? If so, what specific brand unit/model number did you use?

    I'd like to mix the supply water down from around 190 degrees at the Garn to about 140 degrees. I plan to use the return water to mix with the supply water. At this point, I have no idea what my return water temp will be. I'm guessing it will still be over 100 degrees (a complete guess). I'm planning on a three way valve that would be hooked up with either 1 1/2" or 2" threaded black pipe.

    If you mixed your supply down by using your return water, then please tell me how you did it and what mixing valve you used.

    So far I've got quotes for $600 and $800. That just sounds really steep.

    The setup is for a forced air furnace, with three separate zones. I'll also be heating DHW.

    Thanks for the input.

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  2. curtis

    curtis Member

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    Why would you want to bring your supply temp down to 140 for a water to air heat exchanger in your furnace plenum?
  3. Frozen Canuck

    Frozen Canuck Minister of Fire

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    Agreed no need for a mixing valve. Do however install a tempering valve on your DHW tank to avoid scalding anyone.

    In a forced air situation if you can bring the water into the coil at 190 so much the better. Closer to the temp of a fossil unit than 140 would be.
  4. sjfrench

    sjfrench New Member

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    A few reasons I'd like to bring down my supply temp:

    1. I'm using a forced air system. The Garn can produces up to 190-200 degree water. If I'm running that through my exchangers, the floor registers run the risk of being piping hot. I've got a three year old in the house, and worry a bit about how hot the registers will get. Most building codes are around 140 degrees.

    2. I'm also running the Garn through two domestic hot water tanks. DHW tanks are not equipped to handle temps that high. I've had a couple of plumbers say that it will ruin the tanks. Not sure why, but I'm assuming they have a sold reason. In addition, I risk safety issue with children using the hot water if it's being heated with a constant flow of 190 degree water. There's hot water...and then there is scalding water. For safety, I'd like to bring that temp down some.

    3. If I only need 150 degree water, then I can use less of my btu's by using less water from my storage. Instead of pulling 190 degree water, I'm pulling 190 ad mixing it with the return. That means I'm using less of my storage.
  5. Frozen Canuck

    Frozen Canuck Minister of Fire

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    Suggest you set your max temp controlled by an aqua stat on the garn to 180 as if your target is 200 it wont take much of an overshoot for you to be producing steam, something to definitely be avoided in a hot water boiler.

    My system ran with 180 max water temp & this was never an issue, warm to the touch yes burning hot no. My HX were 2x what the chart said I should aim for so unless yours are even more than 2x design need, I really can't see it.

    Ok for clarity, it sounds like you are running boiler water directly into the DHW tanks (a very bad thing) the boiler water & your DHW should be separated by a HX (heat exchanger) the aqua stat on the DHW tanks control a small pump that mixes the DHW on one side of the HX & controls how hot the DHW can get via the aqua stat by turning the small pump off & on.

    An HX with a pump controlled by the aqua stat on the DHW accomplishes this safely. You control how hot the DHW is via that aqua stat.
  6. TCaldwell

    TCaldwell Minister of Fire

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    two years ago I repiped my garn as you are describing, I used a taco ivalve 3 way right behind the garn before the hx. The piping from the garn to the hx was 1.25 black iron, the ivalve with 1inch. I found the best place for the supply temp sensor being on the house supply manifold. I tried setpoints from 130 to 160, overall the valve worked well,but for my house with primarily fin tube baseboard it was not a good choice. Taking the supply temp at the garn of say 190 reccomended max mixing down the supply temp to 140 at the valve then losing another 5 to 10 deg at the house supply side of the hx really limited the usefulness based on my emitters. I removed and repiped direct drive, I will sell it cheap.
  7. sjfrench

    sjfrench New Member

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    This was a great help. Thank you for the input. Based on your recommendations, I think I'll skip the mixing valve completely and just use the aqua stat at the DHW. If people with real world experience are saying that the registers don't get too hot, then I'll trust that experience.

    Another question, do you run your pumps continuously to circulate during the heating season, or do you have them set up with relays to run on demand?
  8. TCaldwell

    TCaldwell Minister of Fire

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    The first year I had the garn pump run all year and another pump to keep the oil boiler hot for dwh all year and the zone pumps on a call for heat. This churned alot of heat unecessarily. I replumbed with a indirect fired hwh as another zone so i was able to pipe parallel rather than in series, allowing the oil boiler to go cold. Now the garn pump and loop pump and any zone pump energize only with a heat call, works much better.
  9. heaterman

    heaterman Minister of Fire

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    There is no need for a mix valve on a high temperature system like your furnace. If you were doing radiant floors or something that needed 100-120* water, then yes, use a mix valve there.
    The Garn itself does not need it and the coil in your furnace will perform much better at temps >140* than <140*.
    I have heard a few "reasons" stated for use of a mix valve right off the Garn but nothing that would compel me to do so.
    sjfrench likes this.
  10. sjfrench

    sjfrench New Member

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    You all just saved me a ton of cash. I'm passing on the mixing valve. I will take the advice on the aqua stat on the DHW. Greatly appreciated.

    I am still wrestling with the pumps doing continuous flow vs. on demand.

    We ran 600' of 1" pex today - I'd been dreading it - it was not nearly as bad as I thought. Just. 100' to go and the pex is done!
  11. heaterman

    heaterman Minister of Fire

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    600' of 1"??????
    Is that your loop from the Garn to the house?
    Coal Reaper likes this.
  12. Coal Reaper

    Coal Reaper Minister of Fire

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    What circ are you planning to run? Insulation plan?
    I have been very happy with my bumble bee. I have it run only when there is a call for heat. It cranks full force for three minutes to clear the lines and then backs off to maintain a set point. You can also do deltaT. I questioned whether it would have enough balls to move the btus required, but so far it always just runs on lowest speed and works fine. Returns 140*f to storage. Idk about 600'of 1" though...
    How many garn users actually fire to 200*?
  13. sjfrench

    sjfrench New Member

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    Here's the set up. I have four zones (three heating units and one DHW - two tanks). I'm running each specific zone as it's own loop (supply and return) to the Garn barn. So that means 8 individual runs of pex. Heaterman, I know you are a pro, I'm over explaining in case someone reads this later. Each zone pump is at the manifold, and the manifold will be in the Garn barn. Maybe this isn't typical, so let me explain why we chose to do it that way.

    First up, the house is 8500 sq feet and is built "long" because it overlooks a river in back. We had to build the Garn barn on the east side of the house so that it wouldn't block the view.

    I'm about 16 ft off the east side of the house with the Garn barn. Each loop (supply and return) from the Garn barn, goes to the house and enters through a crawl space. Most of the house is over a basement, but there is a section of the house that has a crawl space. Here's where it gets expensive. Once I run the initial 16 feet underground and come into the crawl space, each loops goes in a totally different direction. One heating loop heads 25' south into the garage for an upstairs bonus room heating unit, one loop heads 35' north and down for a basement heating unit, and two loops head a ridiculous amount west for a DHW and a heating unit.

    So why not just run a primary loop from the Garn barn to the house and set up a manifold with the pumps in the house. Because ultimately, the next best place to put the manifold was in the garage, and it didn't save me any distance when I've still got a pex run from a pump to each zone. Basically, the garage is the same distance from the other zones as the Garn barn.

    I could have saved money in a couple of areas. For example, I could have put the manifold under the house in the crawl space. That alone could have saved me about 150' of pex, because I would have only had one loop from the manifold to the Garn barn instead of four loops. However, I didn't want the pumps and the manifold under the house in the crawl space. I wanted it somewhere where we would have easy access for any repairs. We are using the Garn barn to hold all the mechanical. The crawl space is only about 3-4' high. Just not an ideal working space. So, since everything had to be consolidated at a manifold, that was going to be in the Garn barn or the garage. They are both the same distance from the other zones, so we just decided to consolidate everything in the Garn barn.

    I could have also saved pex in another area by consolidating two of the zone loops into one single loop. We have two runs that are parallel for a good distance, those zones are for DHW and the furthest heating zone to the west. We could have made one long run, then split off the DHW and send a supply/return to the furthest heating unit and then back. Basically the DHW is "on the way" to the furthest heating unit. It would have saved a lot of money on pex. Dang, those are long runs!

    I'm passing on combining for two expensive reasons. First, if anything happened to me, I want a system that is super convenient for my wife and easy potential home-buyer to understand. My wife is a real smart lady, and that's not a slam on her. I want a system that isn't threatening or complicated for a potential home-buyer. It's just easy to say, "when it warms up in the spring, go to the Garn barn, and shut off these three valves and pumps that feed the heating system"...done. Not, go up on an eight foot step ladder, see those valves in the ceiling, turn them off, then go to the Garn barn and turn off these two valves and pumps. At the end of the day, it's another $200 in pex and a $80 pump to have them all terminate in the Garn barn and it makes the set up very easy to understand and super simple to run. Heck...I'm dropping over $20,000 on this entire set-up, I'm not going to nickel and dime over $300. Fortunately, we've done all the labor so far, so we are staying under budget, and you just saved me from buying a mixing valve! Secondly, in the summer, any pex line connected to the DHW is going to carry heat into my flooring. If I split off the DHW, the pex would run through the basement ceiling (upstairs flooring). I know we could install bypass valves that could be shut off...that takes me back to the first reason. I also wanted to make that DHW run as short and direct as possible since I'm running DHW year-round. I'm trying to keep it out as much radiant heat as possible on that DHW run. I'll shut down all three heating zones completely, and only run DHW in the summer.

    A few nice things things that have worked our for us. We've been able to run each loop with zero fittings. Pex isn't known to fail, but when it does, it is almost always at a fitting. Since the manifold is in the Garn barn, I was also able to bypass the expense of a $250 primary loop pump. Another nice feature, when the house was built, they put an exterior exit off the man's master closet on the east side. It's basically a separate mud room in the man's master closet. That door opens up onto a deck (yet to be built) that will go right out to the Garn barn. Sure makes for easy access.


    [​IMG]
    It's a work in progress. ...and we are making progress.

    Hopefully this makes sense. Heaterman - thanks for all the input you've provided on other posts. I've read nearly all of them!

    Attached Files:

    Last edited: Nov 10, 2013
  14. sjfrench

    sjfrench New Member

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    I wondered about the bumble bee pumps. I ended up going with four Taco 0015-IFC pumps.

    Insulation - R-19 in the walls of the building - R-30 in the ceiling, blue foam board underneath the Garn - but I haven't insulated the actual Garn unit at this time. Hope to do that next week. Trying to decide if spraying on closed cell foam would hold up as the unit heats and cools. Still undecided how to insulate the actual unit.

    Underground piping is 36" deep. Buried in 8" PVC water line and surrounded by sprayed in closed cell foam.
    [​IMG]

    Here's the line being sprayed. The green is the 8" PVC water line - it holds the pex runs. The ditch was completely filled with closed cell foam. The white pipe is for future data lines and any other line I might want to pull. The gray PVC is for electric. I tried to keep the data and the electric separate to avoid interference.

    I'm not planning on firing to 190* or 200* on a regular basis, I just want to make sure my mechanical could handle a system that hot in case I made a mistake. I think I'll set a goal of firing around 170-180*.

    Attached Files:

  15. heaterman

    heaterman Minister of Fire

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    Makes sense to me. Carry on. :)

    I just saw the "600' of pex" thing and thought OH NO!!!! ..... here comes another poor guy frying a 0013 or two every winter, trying to push 10gpm through 30 ft of head....

    If you want a Garn "sweater" insulation kit give me a shout. The fabrication company in Chicago can ship it directly to you.
  16. sjfrench

    sjfrench New Member

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    What is a Garn "sweater" insulation kit. I remember you referencing it an older post, but forgot about it. Where do I go to find info and pricing?
  17. heaterman

    heaterman Minister of Fire

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    I worked with Fabrication Specialties from Chicago to design an easy to install insulation kit for a Garn in 2009-2010. It takes maybe 30 minutes to install and does a pretty passable job of keeping the heat in your Garn.

    Attached Files:

  18. sjfrench

    sjfrench New Member

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    I'm interested in learning a bit more. Sure looks easy to install...and I'd save some money if I don't need to build the metal-stud wall to enclose the Garn. What does the R-value compare to? What does it cost? Is there a website where you order?
  19. jebatty

    jebatty Minister of Fire

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    You have a very exciting project and I bet you can't wait to fire it up. The Garn is a good boiler and very easy to operate. I saw from another thread that you chose the Garn 2000 and that you are using three water to air hx's for your 8500 sq ft space heating, plus one zone with two dhw tanks. Also that you determined you can use water down to 140F, and normally plan on firing the Garn to 170-180F. Correct this if I misread anything.

    Now for a few questions, the answers to which should help you avoid some mistakes as you finish the install; maybe more questions later. Did you determine your heat loss/demand requirements for each of your zones, and if so, what might they be? Or did you determine total heat loss/demand requirement and what was it? Unpressurized system? Pressurized, and if so what is your plan for the unpressurized/pressurized? Are you using one or more plate hx's to the pressurized side; what size of each? What gpm flow at what temp do each of the water to air hx's need to produce their rated output? What pump head in each zone? What circ(s) are you using for each zone? Are your dhw tanks indirect or are you using a plate hx?
  20. sjfrench

    sjfrench New Member

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    I worked with my Garn rep to determine the size exchangers I needed. We didn't do a total house heat loss calculation. He had me go through and look at each of my forced air furnaces and give the btu ratings on each of the three units. We then gave him the plenum sizes and he had the exchangers built and shipped.

    Unpressurized. The local term for my system is central heat and air. Not sure what you all call it up north, but that's the term in our area.

    I don't know yet. The Taco 0015-IFC pumps are all variable speed, so I'm hoping for a season of trial and error. I'm planning to generate at around 180 degrees. I'll need to see what my temp drop ends up being at each exchanger and then look at adjusting the speed of the pump to compensate for loss.

    The Garn will have all pumps and manifold installed in the building. I have one zone that is about three feet above the manifold. The other three zones will be about 8 feet below the manifold. I haven't calculated the acutal pump head requirements. Each pump is only responsible for one zone and I'm running 1" pex throughout the entire system.

    I'm not sure I understand what you are asking here.

    We are using a sidearm exchanger. Not ideal, but it will work. I wanted new DHW tanks with the built in coils...but alas...too expensive.
  21. maple1

    maple1 Minister of Fire

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    We are using a sidearm exchanger. Not ideal, but it will work. I wanted new DHW tanks with the built in coils...but alas...too expensive.

    If you plan to heat your DHW from storage in the non-heating seaon, you'll likely be disappointed with the sidearm.
  22. jebatty

    jebatty Minister of Fire

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    1) It would be good for you to know the specs on the water to air hx's. The specs would tell you btuh output based on a supply and return temperature, gpm flow rate, and pressure drop. That along with the round trip length of your 1" pex would give you the info you need to make a pretty good calculation of pump head at the specified flow rate, and then you also would know whether or not the 0015 could deliver that volume of water.

    2) With one zone about 3 feet above the manifold and the others below, I'm assuming that the Garn water tank level is above the plumbing in all zones. Unpressurized probably should work OK unless for some reason a flow rate is required that might cause cavitation due to lack of sufficient pressure based on temperature. I assume Garn knew the facts about your install and the decision to go unpressurized.

    Continuing good luck on your install. Keep us posted, especially when you fire up and get your first of many warm days and nights.
  23. sjfrench

    sjfrench New Member

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    It's not to late for me to adjust for the DHW. What would you recommend?
  24. maple1

    maple1 Minister of Fire

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    I'm not sure I can say with certainty.

    Likely (I hope) a plate exchanger, pumped both sides.

    I just know I was disappointed with my sidearm this summer. Seemed once storage got below 150 or so, it didn't do much good. Granted, I might have been able to improve things by pumping the domestic side of it too, but working on convection I have about a 30° difference between supply hot in & domestic hot out. It works fine the rest of the time (when burning for heat as well).

    I have a plate HX on the way (I think, it's been a couple weeks since I ordered it), and a B&G Ecocirc ready to put in with it. I plan to just add it in, above the sidearm, for an easier install. Now that it's heating season again, it's slipped a bit on the priority list. I've had my new system up & running for a bit over a year yet, and it's still not finished.
  25. heaterman

    heaterman Minister of Fire

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    One extremely simple way to do domestic water is to tee a flat plate HX into the cold water line entering the heater, IF you can tap into a loop in your system that is constantly circulating.

    Tee out of the incoming cold line, into the HX then back out of the HX and into the HWH. Leave a bypass in place so you can isolate the HX in the summer if not using the wood boiler.
    Incoming cold water is now heated from ground water temp up to 110-120*+ depending on the size of heat exchanger you are using. Your water heater now has to do nothing but maintain temp of the tank so 90% of the load is gone. No extra pumps, no controls, no wiring, just pre-warmed water going into the tank.

    We used a 10 plate on a job like that a couple weeks ago and the incoming water was 140* with a boiler water temp of 160*. It would maintain that with 2 faucets running but when we turned on the tub + the kitchen and bath faucets the water temp fell to about 120*. Still not bad for such a simple install. About $35 in fittings/ball valves + the cost of the 10 plate which was around $190 or so.
    Going to an aquastat controlled system and a pair of pumps to circulate both sides of the HX will run around $4-500 + the HX.

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